This invention relates to a method for the manufacture of polymer-impregnated hollow concrete products.
Japanese Pat. Publication No. SHO. 49(1974)-34757 and SHO 51(1976)-22493 disclose that concrete products in which the fine voids thereof have been impregnated with a monomer and this monomer has been thermally polymerized in situ enjoy improved bending strength and compressive strength and, at the same time, exhibit outstanding resistivity to freezing and thawing and to chemicals.
The conventional method for polymer impregnation, comprises the steps of drying, with hot air, molded concrete article released from its mold, deaerating it under a reduced pressure, impregnating it with a monomer under application of pressure, thermally polymerizing the monomer entrapped within the concrete article and giving a surface treatment to the concrete article.
The hot-air drying of the molded concrete article is aimed at vaporizing the moisture entrapped in fine voids of the concrete article and securing spaces for impregnation by a monomer, enhancing the adhesiveness of the concrete with the polymer and, at the same time, obtaining the polymer in a continuous phase and preventing the monomer entrapped within the fine voids from being dispersed and wasted owing to an increase in the vapor pressure within the fine voids during the thermal polymerization of the monomer.
The vacuum deaeration of the dried concrete article is aimed at accelerating the speed of the monomer impregnation of concrete article and shortening the time required for the impregnation, increasing the ratio of monomer entrapment by allowing the monomer to be amply diffused even into fine voids at great depth and, during the thermal polymerization of the monomer, preventing the entrapped monomer from being dispersed and wasted owing to the thermal expansion of air.
As the monomer for impregnating concrete products there is chiefly used methyl methacrylate or styrene. Optionally the monomer is used with a plasticizer, a crosslinking agent, a polymerization accelerator, etc. incorporated therein for the purpose of improving the quality of the concrete products. In most cases, the impregnation of the molded concrete article with the monomer is effected by a procedure comprising the steps of deaerating the concrete article and subsequently causing the deaerated concrete article to be impregnated with the monomer under application of pressure to accelerate the diffusion of the monomer into the concrete article.
The manufacture of polymer-impregnated concrete products according to the method described above necessitates use of facilities for drying molded concrete articles, tightly closed vessels for vacuum deaeration and impregnation under pressure, and facilities which, during the thermal polymerization of the entrapped monomer, permit the monomer to polymerize without being dispersed and wasted. Further, the facilities and vessels mentioned above are destined to grow both in direct size and price in proportion to the size of the concrete products to be treated.
In the known method of manufacture of polymerimpregnated hollow concrete products, the hollow molded concrete article is introduced into a monomer vessel to impregnate it with the monomer. After the hollow concrete article has been impregnated with the monomer, it is taken out of the monomer vessel. At this time, the excess monomer solution not impregnated into the concrete that remains in the hollow part of the concrete is removed from the vessel together with the article and is consequently wasted. Even if such excess monomer solution is recovered somehow or other, the recovered monomer solution frequently contains cement powder and other dust from the molded concrete. Before it is put to use again, therefore, it must be freed from such extraneous matter.
The inventor has proposed a method for the manufacture of concrete products of excellent mechanical properties, by the steps of filling a frame capable of withstanding high temperature and high pressure with a concrete mix in such a manner as to form a concrete article, then airtightly closing the frame, heating the frame while preventing leakage of water from the molded concrete article within the frame and allowing the content of the frame to cure under conditions of high temperature and high pressure (U.S. Pat. No. 4,224,274). The present invention constitutes a further development of the method described above.